Vehicle wheels sometimes experience misalignment. Impacts from the road along with general wear and tear can cause "wheel misalignment" where a tire touches the road at an undesirable angle. This, in turn, affects the control of the vehicle and rapidly wears the tire. Typically, when wheel misalignment occurs, the vehicle in motion steers towards one side, forcing the driver to counter-steer the vehicle in the opposite direction in order to compensate for the misalignment. In such a situation, the vehicle should be "realigned" to have the proper tire orientation restored.
For efficient operation, vehicles require routine adjustments to wheel alignments. Various factors are relevant to wheel alignment including: turning radius, axle caster, wheel camber, king pin inclination, and wheel toe-in/toe-out. Each of these factors, explained below, must be taken into account to achieve minimum tire wear, maximum component life, and ease of steering.
The turning radius is the radius ol the arc created by the center of the vehicle track for the outside front wheel when making the shortest turn. Caster angle is the inclination in degrees that the top of the king pin leans towards the front or rear of the vehicle with respect to the vertical. Typically positive caster is used, which places the axis of the king pin ahead of the point of road contact. This causes the wheels to want to roll straight ahead, thus achieving maximum directional stability. Wheel camber is the amount in degrees that the front wheels incline or tilt away from the vertical plane when all of the wheels are resting on a level plane and in the straight ahead position. Camber places the road contact point closer to the axis of the king pin to reduce axle stresses. King pin inclination angle is the amount in degrees that the top of the king pin is inclined from a vertical position towards the chassis centerline at the top and away from the centerline at the bottom. Wheel misalignment occurs if any of these factors are out of specification, however, most misalignments generally involve toe in/out of the steering axle.
When viewing the front axle and wheels from the top, if the front of the wheels are closer to each other than the back of the wheels, this is called toe-in. If the front of the wheels are farther away from each other than the backs of the wheels, it is called toe-out. Typically, because of camber, the wheels are adjusted for toe in so that when the vehicle is in motion the wheels will remain parallel with the vehicle. If the toe-in is not in the correct adjustment position, vehicle steering is affected and tire wear is increased.
Presently, to determine whether, and how much wheel alignment adjustment is necessary, a worker either manually estimates or electronically determines the toe-in/out measurement while the vehicle is stationary. Then, the worker manually adjusts the steering components to correct the misalignment in order to establish the correct toe-in position for the tires.
Although this present method of determining the wheel misalignment of a vehicle has been used for years, this method is somewhat time consuming and sometimes inaccurate. In large part this is due to a misread of the toe-in measurement prior to adjustment, or an improper configuration of an alignment measurement device.